Release compositions are used, for example, to coat papers or films that are used as release backing sheets overlying the pressure-sensitive adhesive layer used in pressure-sensitive adhesive (PSA) products such as labels, decals, tapes, etc. The pressure-sensitive adhesive adheres to the release coated surface of the release liner sufficiently to enable the pressure-sensitive products to be handled prior to use. The liner is removed immediately prior to application of the pressure-sensitive adhesive product to another surface.
Furthermore, the release liner serves to facilitate cost-effective manufacture of rolls or sheets of pressure-sensitive products such as labels. It also functions as a carrier for labels for dispensing in automatic labeling operations and for computer printing and various applications. The performance attributes of a release liner are critical to both the manufacture and end-use application of pressure-sensitive adhesive products.
Typically, the release liner is provided as a silicone layer on a support layer having high hold out (i.e., the support layer on which the silicone layer is deposited is resistant to silicone penetration). The paper substrates typically utilized for producing release liners include super calendered Kraft paper, glassine and clay coated (coated one side or coated two side) products.
Silicone release systems can be applied to a suitable substrate using either solvent based or solventless formulations. Conventional substrates typically exhibit good silicone holdout, but only medium to poor levels of silicone cure. Incomplete cure of the silicone coating can result in unreacted silicone compounds in the release liner that can migrate onto an adjacent surface such as an adhesive or the back side of the support substrate. For example, unreacted or non-crosslinked silicone compounds present in a partially cured silicone release layer can migrate onto an adjacent adhesive layer and reduce its adhesive properties. Silicone migration or volatilization is also problematic for silicone-sensitive end uses. Silicones can transfer to the back side of the liner substrate stored in roll form resulting in a surface that is difficult or impossible to print. Moreover, any uncured silicone that transfers to the back side of the support substrate can re-transfer to another substrate which has been adhesively or otherwise laminated to the release liner. This re-transfer of uncured silicone can also cause printing problems such as poor adhesion or non-wetting of the ink.